"The Hobart 135 or 175 do not come with a cart with wheels & the 140 also has a spot, stitch & pause timer which are ideal for thin gauge sheet metal welding. "
WHOOP DE DOO! In over 40 years of burnin welding rods & wire, I have yet to see a factory cart that was worth a fart in a windstorm. That includes Miller, Lincoln and P&H.
Lets come at this from a different viewpoint.
The guy telling you all about his spot & stitch timers is peddlin you crap you will never use. My Miller 225 is over 20 years old, and has spot and stitch capability, it's called the trigger on the gun, and it's operated by a weldOr behind the hood. Unless you are planning to run the machine on a robot, spot and stitch are useless functions.
20% duty cycle means you can weld 2 minutes out of every 10 minutes without overheating the machine. For the average guy, this will pretty much work out since welding usually involves more time setting things up to be welded than it does actually welding.
Welder manufacturers, battery charger manufacturers, and Chinese Prisoners can all build something that looks like a welder, and all of them have figured out they can sell a lot of unneeded crap to people who think they can buy a machine and instantly become a weldOr. There are more of these machines sold to sit in garages unused than I could count, and while they are good for the economy and the bottom line at the box store, less than 1% of them are good for the guy who paid for them. I see more postings on how to preset the machine than I can count, from guys who bought a box, and who will never make a decent weld, because they believe the weld comes from the machine.
There's an old joke about teaching a chimp to weld with a MIG, and it is fairly true, BUT, welding is dangerous. If you make a bad weld it will break, and it will break at the worst possible time, sometimes killing people. I've watched a guy loose a trailer because he "welded" his hitch. The weld sure looked good, BUT, it wasn't a weld. MIG welds are deceptive, especially when done by unskiller operators.
BEFORE you buy any welder, go learn the basics of welding at your local community college or VoTec. At the very least, you'll come away with some idea of the process, and possibly even an understanding of machines. Then, go establish a relationship with a local welding supplier who will let you try machines before you buy them. The dollars "saved" buying a machine over the internet will be forgotten long before the greif of not having a supplier who will be there to help you.